A rectangular film of liquid is expanded from ( 6 cm × 5 cm) to ( 8 cm × 9 cm). If the work done is 4 × 10⁻⁴ J, the surface tension of the liquid is (a) 0.04 N/m (b) 0.05 N/m (c) 0.06 N/m (d) 0.07 N/m

Answer: (b). Film has two surfaces: W = 2TΔ A. Δ A = 72 - 30 = 42 cm² = 42×10⁻⁴ m² T = 4×10⁻⁴2 × 42×10⁻⁴ ≈ 0.048 ≈ 0.05 N/m So the answer is (b) 0.05 N/m.

A rectangular film of liquid is expanded from ( 6 cm × 5 cm) to ( 8… | MHT CET 2026 (12 May, Shift 1)

Q9MHT CET 2026 · 12 MAY · SHIFT 1Medium

Surface Energy & Work Done

A rectangular film of liquid is expanded from ( $6$ cm $\times 5$ cm) to ( $8$ cm $\times 9$ cm). If the work done is $4 \times 10^{-4}$ J, the surface tension of the liquid is

Show answer and solution

Answer: (b)

Film has two surfaces: $W = 2T\Delta A$ .
$\Delta A = 72 - 30 = 42\text{ cm}^2 = 42\times10^{-4}\text{ m}^2$
$T = \dfrac{4\times10^{-4}}{2 \times 42\times10^{-4}} \approx 0.048 \approx 0.05\text{ N/m}$
So the answer is (b) $0.05\text{ N/m}$ .

Report a mistake

Surface Energy & Work Done question from MHT CET 2026 (12 May, Shift 1)

More questions on Surface Energy & Work Done